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Last modified
1/26/2010 10:08:01 AM
Creation date
10/5/2006 4:04:55 AM
Metadata
Fields
Template:
Floodplain Documents
County
Logan
Community
Sterling
Basin
South Patte
Title
Sterling Flood Control Interceptor Channel Project
Date
4/1/2002
Prepared For
Sterling
Prepared By
URS
Floodplain - Doc Type
Project
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />SEmOITHREE Anected Environments and Environmental Consequences <br /> <br />basin has an area of 645 square miles. Upon entering the floodplain of the South Platte River, <br />the gradient of Pawnee Creek becomes quite low. This condition contributes to flooding on <br />Pawnee Creek in the vicinity of CR 31 and CR 33, with a recurrence interval of almost once <br />every lO years. When this occurs, overbank floodwater on the south side of the creek flows <br />overland in the general direction of Atwood. The overbank flow on the north side of the creek <br />flows overland in the general direction of Sterling. These overland flows, as they are transported <br />lower in the basin, are physically separated by topography features from the floodwater <br />associated with Pawnee Creek. Therefore, these two split flows contribute to separate flooding <br />situations. Factors that contribute to flooding at each location are outlined below. Generally, <br />flooding is attributed to conveyance constrictions created by road, highway, and/or railroad <br />embankments. <br /> <br />Presently, the Highway 6 and UPRR bridges over Pawnee Creek have the capacity to convey <br />approximately 1,800 cfs. Water in excess of the three bridges' conveyance capacity is ponded <br />upstream of the bridges and/or pushed north along Highway 6 into Sterling. The water remains <br />pooled upstream of the bridges until the inflow of Pawnee Creek is reduced below l,800 cfs. <br />Overland flow on the north side of Pawnee Creek enters the northwestern side of Sterling and <br />unites with water from the Sand Creek Drainage as it flows through the residential and business <br />districts of the city on its way to the South Platte River. Water that flows from Pawnee Creek <br />along Highway 6 also enters the western side of Sterling and follows existing drainage systems <br />through residential and business areas ofthe city prior to flowing into the South Platte River. <br /> <br />Federal Water Pollution Control Act (FWPCA) Amendments of 1972 created the system for <br />permitting wastewater discharges (Section 402), known as the National Pollutant Discharge <br />Elimination System (NPDES). The Clean Water Act prohibits the discharging of pollutants <br />through a point source into a "water ofthe United States" without a permit. In 1990, the Phase I <br />Storm Water regulations addressed construction activities that disturbed five or more acres of <br />land as Category (x) of the definition of "storm water discharges associated with industrial <br />activity" (40 CFR l22.26(b)(14)(x)) (EPA 200l). These activities require an NPDES <br />Construction Storm Water Permit be obtained. <br /> <br />3.9.1 Alternative 1. No Action <br /> <br />No activities would occur with the No Action Alternative; therefore, this alternative would not <br />affect the hydrology or water quality of Pawnee Creek or the South Platte River. <br /> <br />3.9.2 Alternative 2 - Sterling Flood Control Interceptor Channel (Proposed Action) <br /> <br />This alternative would prevent flood flows up to the lOO-year flood event from entering Sterling <br />and, thus, significantly decreasing the potential for flood damage within the city (ICON 2001). <br /> <br />Even for flood events, which exceed the design event, this alternative would substantially reduce <br />flooding in Sterling. In addition to less flow, the duration of flooding would be reduced. With <br />this alternative, flows in the South Plate River between the channel's outfall and Sterling could <br />be increased by up to 5,000 cfs. Preliminary evaluation indicated that this discharge into the <br /> <br />3-13 <br />
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